If petrol is accidentally spilt over the tank during a fill-up allow it to dry and do not wipe it off, it tends to soften the protective varnish over the gold lines and wiping whilst wet will remove the varnish and allow the gold to deteriorate.
Enamelled parts must never be wiped over when dusty or muddy as this will dull the lustre of the enamel. All dirt should be floated off with generous supplies of water and a sponge or soft cloth. A little household detergent powder can be mixed with the water if there are greasy patches to be cleaned.
When clean use a good polish to restore the brilliance such as "Chemico 49" (makers, The County Chemical Co., Ltd., 561, Stratford Road, Shirley, near Birmingham).